I’m one of the founders. The environments notebook includes the default environments you get when starting a notebook on Nextjournal. These are again built in Notebooks, see e.g. for https://nextjournal.com/nextjournal/python-environment for a description of what our default Python environment contains and how it is built. This is again built on top of our bash environment, that’s built on top of a stock ubuntu image: https://nextjournal.com/nextjournal/bash-environment.